1. Field of the Invention
This invention relates to signal transmission means for giving and taking signals between an alidade portion and a fixed portion in a survey instrument having an alidade portion and a fixed portion rotatably holding the alidade portion.
2. Description of the Prior Art
Recently, along with the introduction of electronic techniques into various optical instruments, there have come to be seen in the field of survey instruments the devices in which electronic parts are combined with optical parts. There are theodolites which utilize a rotary encoder to obtain an electrical signal corresponding to the angle of rotation of a telescope and there are also tachymeters which effect distance measuring and measurement of angle and put out these as electrical signals. Each of these survey instruments comprises an alidade portion having a measuring portion consisting of a telescope or the like, and a fixed portion rotatably holding the alidade portion. In such a survey instrument, there are the following measures for taking out and recording the measured electrical signals:
(a) providing the alidade portion with a recording device; PA1 (b) connecting together the alidade portion and the recording device by means of a cord; and PA1 (c) transmitting the electrical signal from the alidade portion through a slip ring to a lower board (which is a part of the fixed portion) and connecting the lower board to the recording device by means of a cord. PA1 (a') Since the alidade portion becomes large, the entire survey instrument is unstable and weak against vibration and wind or the like. PA1 (b') During the operation, the cord clings to the instrument and reduces the operability. PA1 (c') Unsatisfactory contact is likely to occur at the portion of the slip ring.
However, these instruments heretofore proposed have their own disadvantages, as shown below.